The invention lies in the field of integrated technology and relates, more specifically, to an integrated circuit configuration, that is to say a circuit configuration which is arranged in a substrate, with at least one capacitor.
An integrated circuit configuration of this type is described, for example, in European patent EP 0 415 530 B1 (see U.S. Pat. Nos. 5,126,810 and 5,196,365). The integrated circuit configuration is a memory cell arrangement wherein a memory cell comprises a transistor and a capacitor. The capacitor is embodied as a stacked capacitor and comprises a polysilicon structure with a plurality of polysilicon layers which are essentially arranged parallel one above the other and are connected to one another via at least one lateral support. The polysilicon structure is formed by the alternate deposition of polysilicon layers and SiO2 layers, which can be etched selectively with respect thereto, on the surface of the substrate, patterning of the sidewall, production of layers coverings (spacers) made of polysilicon on at least one sidewall of the layer structure and selective etching-out of the SiO2 layers. The polysilicon structure acts as a first capacitor electrode of the capacitor. The areas of the polysilicon structure are provided with a capacitor dielectric. Afterward, a second capacitor electrode of the capacitor is produced, which adjoins the capacitor dielectric. Despite the capacitor having a small space requirement, that is to say the capacitor having a small area when projected onto the substrate surface, the capacitor has a large capacitance since the surface area of the polysilicon structure is very large on account of the layers that are arranged one above the other.
It is accordingly an object of the invention to provide a method for fabricating an integrated circuit configuration with at least one capacitor which overcomes the above-mentioned disadvantages of the heretofore-known devices and methods of this general type and which, in comparison with the prior art, can have a smaller space requirement yet a high capacitance at the same time. With the foregoing and other objects in view there is provided, in accordance with the invention, a method of producing an integrated circuit configuration with at least one capacitor, which comprises:
providing a substrate having a surface defining a y-axis extending substantially perpendicular to the surface and defining a first height, a second height above the first height, and a third height between the first height and the second height;
producing a central part of a first capacitor electrode of the capacitor to extend from the first height to the second height, by forming a depression in an auxiliary layer applied on the substrate and filling the depression at least partly with conductive material;
after producing the central part, etching the auxiliary layer no deeper than to the third height;
producing a component of the integrated circuit configuration and connecting the component to the central part produced thereabove;
producing a spacer reaching at most to the second height, by depositing and etching back material as part of a spacing means, on uncovered parts of lateral areas of the central part;
growing conductive material, by selective epitaxy, on the central part but not on the spacing means;
depositing further conductive material substantially conformally;
etching back the conductive material to thereby produce from the conductive material
at least one side part of the first capacitor electrode beside the central part and spaced apart from the central part, such that the side part extends from the third height to the second height;
an upper part of the first capacitor electrode on the side part and the central part and connecting the side part and the central part to one another; and
to partly uncover a portion of the spacing means that projects laterally below the side part;
providing the first capacitor electrode with a capacitor dielectric; and
producing a second capacitor electrode adjoining the capacitor dielectric.
The resulting product is an integrated circuit configuration with at least one capacitor wherein the capacitor is arranged above a surface of a substrate. A y-axis runs perpendicularly to the surface of the substrate. A first capacitor electrode of the capacitor has a central part, which extends from a first height as far as a second height situated above the latter, with respect to the y-axis. The central part is connected to a componentxe2x80x94arranged below itxe2x80x94of the integrated circuit configuration. The first capacitor electrode has at least one side part, which is arranged beside the central part and is spaced apart from the latter. The side part extends from a third height, which lies between the first height and the second height, as far as the second height. The first capacitor electrode has an upper part which is arranged on the side part and the central part and connects these to one another. The first capacitor electrode is provided with a capacitor dielectric. A second capacitor electrode adjoins the capacitor dielectric.
The method may also be summarized as follows: The capacitor is produced above a surface of a substrate. A central part of a first capacitor electrode of the capacitor is produced in such a way that it extends from a first height as far as a second height situated above the latter, with respect to the y-axis. A component of the integrated circuit configuration is produced and is connected to the central part produced above it. At least one side part of the first capacitor electrode is produced in such a way that it is arranged beside the central part and is spaced apart from the latter. The side part is produced in such a way that it extends from a third height which lies between the first height and the second height, as far as the second height. An upper part of the first capacitor electrode is produced in such a way that it is arranged on the side part and the central part and connects these to one another. The first capacitor electrode is provided with a capacitor dielectric. A second capacitor electrode is produced in such a way that it adjoins the capacitor dielectric.
Since the capacitor dielectric covers all the areas of the first capacitor electrode starting at least from the third height, and the second capacitor electrode covers the capacitor dielectric, a part of the second capacitor electrode is also arranged between the lateral part and the central part.
As a result of the cutout in the first capacitor electrode between the central part and the side part, the surface of the first capacitor electrode, which greatly influences the capacitance of the capacitor, is enlarged primarily by lateral areas of the side part and of the central part in comparison with a capacitor electrode without a cutout, without the space requirement of the capacitor being increased. The larger the distance between the third height and the first height, the larger the capacitance of the capacitor.
A particularly large capacitance of the capacitor is obtained if the third height is nearer to the first height than to the second height.
The first capacitor electrode can be produced for example with the aid of a spacing means. To that end, an auxiliary layer is produced above the substrate. The central part is produced by producing a depression in the auxiliary layer and filling it with conductive material. The spacing means is formed in such a way that it adjoins lateral areas of the central part and projects laterally away from the central part below the third height. The upper part and the side part are produced in such a way that they adjoin the spacing means. The upper part adjoins the spacing means from above, while the side part laterally adjoins the spacing means and also adjoins from above the part of the spacing means which projects laterally away from the central part below the third height. The part of the spacing means which adjoins the lateral areas of the central part is consequently arranged between the central part and the side part, while the part of the spacing means which projects laterally away from the central part below the third height is arranged below the side part and can project laterally below the side part. Since this part is not covered by the side part at least laterally and possibly also partly from above, the spacing means can be removed by isotropic etching selectively with respect to the first capacitor electrode. The capacitor dielectric and the second capacitor electrode are subsequently produced.
In order to reduce the space requirement of the capacitor it is advantageous to produce the part of the spacing means which adjoins the lateral areas of the central part with a particularly small horizontal thickness. The horizontal thickness of this part of the spacing means is preferably homogeneous, that is to say that this part of the spacing means has the same thickness everywhere.
In order to reduce the space requirement of the capacitor, it is advantageous to produce the central part and the side part in such a way that their lateral areas are essentially parallel to the y-axis.
Given a homogeneous horizontal thickness of the part of the spacing means which adjoins the lateral areas of the central part, the lateral areas of the side part which face the central part follow the course of the lateral areas of the central part at an essentially constant distance from the lateral areas of the central part. Specifically, said distance is equal to the horizontal thickness of the spacing means.
A particularly large capacitance is obtained if the side part laterally surrounds the central part.
However, it is also possible to provide, say, two side parts which do not adjoin one another.
It is possible to provide more than one side part, which are at different distances from the central part. Each of the side parts may laterally surround the central part. A first side part which is arranged further away from the central part than a second side part also laterally surrounds the second side part. The side parts are interleaved in one another.
A first method is described below, wherein a spacing means is used whose part which adjoins the lateral areas of the central part has a homogeneous horizontal thickness.
After the production of the central part, the auxiliary layer is etched no deeper than as far as the third height. By depositing and etching back material, as part of the spacing means, a spacer is produced on uncovered parts of the lateral areas of the central part. The spacer reaches at most as far as the second height, so that at least one upper horizontal area of the central part is uncovered. The part of the spacing means which is produced as a spacer consequently adjoins the lateral areas of the central part and has an essentially homogeneous horizontal thickness. Material below the third height serves as a further part of the spacing means. Afterward, conductive material is grown by selective epitaxy in such a way that the conductive material grows on the central part but not on the spacing means. Further conductive material is deposited and subsequently etched back, so that the upper part is produced from the epitaxially grown conductive material and the side part is produced from the deposited conductive material, and the part of the spacing means which projects laterally below the side part is uncovered. Since the conductive material on the upper area of the central part is particularly thick on account of the selective epitaxy, conductive material, which can essentially form the upper part, remains on the central part during the etching back until the spacing means is uncovered.
The material from which the part of the spacing means which is produced as a spacer is produced can be etched back further than the thickness to which the material is deposited. In this case, upper regions of the lateral areas of the central part on which the conductive material can grow are also uncovered. During the etching back of the material, the material which is arranged below the third height, i.e. below the removed part of the auxiliary layer, can also be attacked. This is the case in particular when the same material is involved. Since the side part is to be arranged on the spacing means and the side part extends upward from the third height, the third height is defined by the depth to which the auxiliary layer is etched and the extent to which the material of the spacer is etched back.
By way of example, tungsten or tungsten silicide is suitable as conductive material if the central part is likewise composed of tungsten or tungsten silicide. However, any conductive material which grows on the central part but not on the spacing means is suitable.
The spacing means is composed, for example, of silicon nitride or of SiO2.
A particularly small space requirement of the capacitor is obtained if the depression is produced with the aid of a mask whose opening has dimensions which correspond to the minimum feature size F that can be fabricated in the technology used. Consequently, the central part produced by filling the depression also has a width and/or a length corresponding to the feature size F.
An even smaller space requirement can be obtained if, after the etching of the auxiliary layer, the central part is narrowed by isotropic etching. In this case the width and/or the length of the central part may even be smaller than the feature size F.
As an alternative, the mask used for the depression can be enlarged by spacers, so that the opening of the mask has dimensions which are smaller than the feature size F. In this case, the central part has particularly small horizontal dimensions even without isotropic etching.
Since such a central part has a horizontal cross section which is smaller than F2, the entire capacitor can have a space requirement of only F2.
In order to produce such an enlarged mask, material is deposited and etched back after the production of the mask with the aid of photolithographic process steps, with the result that spacers are produced in the opening of the mask, which spacers enlarge the mask, that is to say narrow the opening. As an alternative, it is possible to fabricate an opening with a smaller cross section than F2 using CARL (chemical amplification of resist lines). In this case, the mask is enlarged by silylation.
If more than one side part is to be produced, then after the production of the side part, a further spacing means can be produced analogously to the spacing means. The further spacing means laterally adjoins the side part. Afterward, conductive material is grown again by means of selective epitaxy, thereby enlarging the upper part. As in the production of the side part, further conductive material is deposited and etched back, thereby producing a further side part. This sequence of process steps can be repeated to produce additional side parts.
A second possibility for producing an integrated circuit configuration with at least one capacitor is described below, wherein a spacing means is used whose part which adjoins the lateral areas of the central part has a homogeneous horizontal thickness.
A further auxiliary layer is produced on the auxiliary layer. The depression cuts through the further auxiliary layer. After the production of the depression, the further auxiliary layer is etched isotropically, thereby extending the depression in the region of the further auxiliary layer. By filling the depression with the conductive material, the central part is produced in the region of the auxiliary layer and a part of the upper part is produced in the region of the further auxiliary layer. The upper part is thus arranged on the central part and projects beyond the central part laterally in all directions. The further auxiliary layer and the auxiliary layer are etched selectively with respect to the part of the upper part anisotropically as far as the third height, so that at least one part of the spacing means is formed from the auxiliary layer below the part of the upper part. This part of the spacing means consequently adjoins the lateral areas of the central part and has an essentially homogeneous horizontal thickness on account of the production of the part of the upper part with the aid of isotropic etching. The side part and a residual part of the upper part are subsequently produced in the form of a spacer by depositing and etching back material, parts of the spacer which laterally adjoin the part of the upper part and lie at the same height as the part of the upper part forming the residual part of the upper part.
The spacing means is produced in a self-aligned manner that is to say without a mask to be aligned, below the upper part and adjoining the central part. The distance between the edge of the non-extended depression and the edge of the extended depression determines the thickness of the part of the spacing means, which adjoins the lateral areas of the central part. Since the isotropic etching of the further auxiliary layer removes material uniformly proceeding from the original depression, the thickness of the spacing means is homogeneous. The further auxiliary layer can be dispensed with if, for the purpose of filling the depression, conductive material is deposited and is subsequently patterned with the aid of a mask in such a way that conductive material likewise remains on the auxiliary layer around the central part and forms the part of the upper part. In this case, on account of alignment inaccuracies of the mask, a homogeneous horizontal thickness of the part of the spacing means cannot be guaranteed. In order that the part of the upper part can be produced with essentially perpendicular edges, it is advantageous to produce on the further auxiliary layer a mask layer, which is cut through by the depression. The mask layer is removed only after the isotropic etching of the further auxiliary layer and before the filling of the depression. This also has the advantage that the thickness of the upper part is determined by the thickness of the further auxiliary layer. If the mask layer is dispensed with, then a thicker further auxiliary layer must be deposited in order to obtain the same thickness of the upper part, since the auxiliary layer is also eroded from above during the isotropic etching.
The following method is suitable in particular for producing a plurality of side parts:
The depression is produced in the auxiliary layer in such a way that it initially reaches as far as the third height. A surface of the auxiliary layer lies higher than the first height. Afterward, layers made alternately of conductive material and of insulating material are deposited, without filling the depression, and etched back. Side parts are produced by the etching back of the conductive material and parts of spacing means are produced by the etching back of the insulating material. The number of layers made of conductive material is equal to the number of side parts produced. A part of the bottom of the depression which is uncovered after the etching back of the last layer made of insulating material is subsequently etched more deeply at least as far as the first height. The as yet unfilled part of the depression is filled with conductive material by depositing conductive material and etching it back as far as above the first height. Conductive material which is surrounded by the innermost spacing means forms the central part. Conductive material which is arranged on the side parts, the spacing means and the central part forms the upper part. Preferably, layers deposited later are etched back further than layers deposited previously, in order that there is better contact between the upper part and the side parts.
By way of example, a part of the auxiliary layer is suitable as a part of the spacing means which projects laterally away from the central part.
In order to accurately set the etching depth when etching the auxiliary layer, it is advantageous to produce above the substrate a stop layer whose upper area lies in the region of the third height and to produce the auxiliary layer above that. The depression cuts through the stop layer. The part of the spacing means which projects laterally away from the central part is consequently the stop layer. The stop layer acts as an etching stop during the etching of the auxiliary layer. The stop layer can also act as an etching stop during the etching back of the material of the side part. In this case, an upper area of the stop layer lies at the third height.
The stop layer, the part of the spacing means which adjoins the lateral areas of the central part and the auxiliary layer are composed, for example, of silicon nitride or SiO2. In order to enable selective etching, it is advantageous if the stop layer is composed of a different material than the auxiliary layer.
The integrated circuit configuration may be a DRAM cell arrangement. By way of example, the component is a transistor which, together with the capacitor, forms a memory cell.
A particularly high packing density of the DRAM cell arrangement can be achieved if the capacitors of memory cells are arranged in rows and columns. In order that the side parts which, considered in vertical cross section, are arranged between the central parts have more space, it is advantageous to produce the central part in such a way that a width of the central part which is parallel to the direction of the rows is smaller than a distance between adjacent central parts of capacitors which are adjacent to one another along the rows. Correspondingly, a length of the central part which is parallel to the direction of the columns is preferably smaller than a distance between central part of capacitors which are adjacent to one another along the columns.
A horizontal cross section of the central part may be, for example, rectangular, in particular square, or circular.
The length or width of the central part may be smaller than the feature size F. For the case of the circular cross section, the width or the length of the central part is the diameter of the cross section. The space requirement per memory cell may be 4F2.
Other features which are considered as characteristic for the invention are set forth in the appended claims.
Although the invention is illustrated and described herein as embodied in a integrated circuit configuration with at least one capacitor and method for fabricating it, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.
The construction and method of operation of the invention, however, together with additional objects and advantages thereof will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings